Waveform generator, system and method

ABSTRACT

A waveform generator configured to generate two waveforms of opposite polarity so as to provide a voltage gain across a load. The waveform generator has a primary side circuit comprising a first inductor. The waveform generator has a secondary side circuit comprising a second inductor, a first output region conductively coupled to the load, and a second output region conductively coupled to the load. The second inductor is inductively coupled to the first inductor. The first inductor is conductively coupled to the first output region so as to supply a first of the two waveforms to the load. The second inductor is conductively coupled to the second output region so as to supply a second of the two waveforms to the load. A system incorporating the waveform generator and a method of driving the waveform generator are also provided.

BACKGROUND

The present invention is directed towards a waveform generator, systemand method. In particular, the present invention is directed towards awaveform generator configured to generate two waveforms of oppositepolarity so as to provide a voltage gain across a load, a systemincorporating the waveform generator, and a method of driving thewaveform generator.

Referring to FIG. 1, there is shown a known waveform generator indicatedgenerally by the reference numeral 100. The waveform generator 100 is anasymmetric waveform generator 100 and includes a Field Effect Transistor(FET) 105 connected to a primary winding 101 of a transformer. Thetransformer has two secondary windings 103, 104 conductively coupledtogether and to ground G. The two secondary windings 103, 104 areinductively coupled to the primary winding 101 of the transformer. Thetransformer is configured to deliver two waveforms 113, 114 of oppositepolarity for providing a waveform voltage gain. In more detail, a DCvoltage source 109 applies a DC voltage to the primary winding 101, anda drive signal switches the FET between ON and OFF states so as togenerate a waveform 111 at the primary winding side. The inductivecoupling between the primary winding 101 and the two secondary windings103, 104 results in two waveforms 113, 114 of opposite polarity beinggenerated at the secondary winding side. The two waveforms 113, 114 aresupplied across a load 107. As a result of the opposite polarity of thetwo waveforms 113, 114, the two waveforms 113, 114 provide a voltagegain across the load 107.

An application of this existing waveform generator 100 is disclose inUnited States Patent Application Publication No. 2016/336159. In thisexisting application, the waveform voltage gain is applied across an ionfilter device.

While the known waveform generator has been successful, it is desirableto improve the performance of waveform generators at high frequenciesand voltages. It is desirable to reduce the effects of parasiticcapacitance on waveform generators. It is desirable to improve thefrequency range within which the waveform generators may effectivelyoperate.

SUMMARY

It is an objective of the present invention to provide a waveformgenerator with improved performance, or at least to provide analternative waveform generator.

According to the present invention there is provided an apparatus andmethod as set forth in the appended claims. Other features of theinvention will be apparent from the dependent claims, and thedescription which follows.

According to a first aspect, there is provided a waveform generatorconfigured to generate two waveforms of opposite polarity so as toprovide a voltage gain across a load, the waveform generator comprising:a primary side circuit comprising a first inductor, and a secondary sidecircuit comprising a second inductor arranged to be inductively coupledto the first inductor, a first output region conductively coupled to theload and a second output region conductively coupled to the load,wherein the first inductor is arranged to be conductively coupled to thefirst output region so as to supply a first of the two waveforms to theload, and wherein the second inductor is arranged to be conductivelycoupled to the second output region so as to supply a second of the twowaveforms to the load.

Here, “voltage gain across a load” means that the amplitude of thevoltage supplied across the load is larger than the voltage supplied tothe waveform generator. The voltage supplied across the load may bebetween 6 and 8 times as large as the voltage supplied to the waveformgenerator.

Here, an element being “conductively coupled” to another element meansthat electrical energy may be transferred between the two elements bymeans of physical contact via a conductive medium. Conductive couplingcontrasts with inductive coupling and capacitive coupling. Theconductive coupling may be provided by a wire, resistor, common terminalor metallic bonding, for example.

Here, an element being “inductively coupled” to another element meansthat a change in current in one element induces a voltage across theother element through electromagnetic induction.

The waveform generator of the first aspect has a first inductorconductively coupled to the first output region of the secondary sidecircuit, and a second inductor conductively coupled to the second outputregion, and at the same time the first inductor and the second inductorare inductively coupled to one another. This contrasts with the existingwaveform generator where there is only an inductive coupling between theprimary side circuit and the secondary side circuit.

The conductive coupling of the first inductor to the first output regionof the secondary side circuit means that there is a current path betweenthe first inductor and the load. This means that current may flowdirectly from the first inductor to the load via the first outputregion.

Surprisingly, by conductively coupling the first inductor to the firstoutput region of the secondary side circuit, the waveform generator ofthe first aspect has been found to reliably produce stable, high voltagewaveforms at high frequencies. It has been found that the waveformgenerator of the first aspect can produce sharp transitions between thetroughs and the peaks of the waveforms. In addition, it has been foundthat the waveform generator of the first aspect has reduced ringingeffects. It has also been found that the waveform generator of the firstaspect is able to operate effectively over a range of frequencies.

Further advantageously, the waveform generator of the first aspect has asimple design because multiple secondary windings are not required. Inaddition, the waveform generator of the first aspect is understood tohave limited parasitic effects, and so is able to operate at low power.The waveform generator may be portable/battery powered.

The two waveforms may be continuous waveforms both having the samepredetermined frequency.

The two waveforms may be supplied to the load at substantially the sametime.

The two waveforms may have a frequency of between 10 and 50 MHz. The twowaveforms may have a frequency of between 15 to 30 MHz. The twowaveforms may have a frequency of 23 MHz.

The two waveforms may have a peak voltage with a magnitude of between0.5 and 1500V. The two waveforms may have a peak voltage of between 100and 500 V. This means that a peak voltage of between 200 and 1000V maybe applied across the load. The two waveforms may have a peak voltagewith a magnitude of between 175 and 250 V. The two waveforms may have apeak voltage that is selected based on the desired voltage to besupplied to the load.

The two waveforms have a duty cycle of less than 50%. This means thatthe generated waveforms are asymmetric. The two waveforms may have aduty cycle of between 20 to 40%. The duty cycle may be selected based onthe desired duty cycle to be supplied to the load.

A first terminal of the first inductor may be conductively coupled to aDC voltage source. A second terminal of the first inductor may beconductively coupled to the first output region. In this way, a currentpath may be formed from the second terminal of the first inductor to theload via the first output region. Current may flow directly from thefirst inductor to the load via the first output region.

The waveform generator may further comprise a switch conductivelycoupled to the second terminal of the first inductor. The switch may bearranged to be activated by a drive signal so as to control thegeneration of the two waveforms.

The switch may be a Field Effect Transistor (FET). The second terminalof the first inductor may be conductively coupled to the drain of theFET. The gate of the FET may be arranged to receive the drive signal.The source of the FET may be conductively coupled to ground.

The waveform generator may further comprise a controller arranged tosupply the drive signal to the switch so as to control the generation ofthe two waveforms.

The waveform generator may be arranged to generate the two waveforms asa result of the switch transitioning from an ON state to an OFF state.

A first terminal of the second inductor may be conductively coupled tothe second output region. A second terminal of the second inductor maybe conductively coupled to ground. In this way, a current path may beformed between the first terminal of the second inductor and the loadvia the second output region. Current may flow directly from the secondinductor to the load via the second output region.

The load may comprise a first terminal and a second terminal. The secondoutput region may be arranged to be conductively coupled to the firstterminal of the load. The first output region may be arranged to beconductively coupled to the second terminal of the load.

The first terminal of the load may comprise a first electrode. Thesecond terminal of the load may comprise a second electrode.

The second output region may comprise a third inductor. The secondinductor may be coupled or conductively coupled to the third inductor.The second inductor and third inductor may be coupled or conductivelycoupled together in series. The third inductor may be coupled orconductively coupled to the load. The third inductor may have a firstterminal coupled or conductively coupled to the first terminal of thesecond inductor. The third inductor may have a second terminal coupledor conductively coupled to the load. The second terminal of the thirdinductor may be coupled or conductively coupled to the first terminal ofthe load.

The first output region may comprise a fourth inductor. The firstinductor may be coupled or conductively coupled to the fourth inductor.The first inductor and fourth inductor may be coupled or conductivelycoupled together in series. The fourth inductor may be coupled orconductively coupled to the load. The fourth inductor may have a firstterminal coupled or conductively coupled to second terminal of the firstinductor. The fourth inductor may have a second terminal coupled orconductively coupled to the load. The fourth inductor may have a secondterminal coupled or conductively coupled to the second terminal of theload.

The load may be an ion filter device.

The ion filter device may be a Field Asymmetric Ion MobilitySpectrometer (FAIMS).

The first inductor and the second inductor may be arranged such thatwhen a voltage of a first polarity is applied across the first inductor,a voltage of the same polarity to the first polarity is induced in thesecond inductor.

The first inductor and/or the second inductor may comprise non-magnetic,thermally conductive coil formers. The non-magnetic, thermallyconductive coil former may help reduce generation of heat in thewaveform generator and improve manufacturing tolerance. The coil formermay be threaded to ensure that the coil is placed in the same place eachtime it is wound. The coil former may be connected to one or more otherheat sink components. This means that the waveform generator may becooled via a direct cooling method, such as a single fan.

The first inductor and the second inductor may have a windings ratio of1:1.

According to a second aspect, there is provided a system comprising: aload; and a waveform generator as claimed in any preceding claimconfigured to generate two waveforms of opposite polarity so as toprovide a voltage gain across the load.

According to a third aspect, there is provided a method of driving awaveform generator as described in relation to the first aspect, themethod comprising: supplying a drive signal to the primary side circuit;and applying a DC voltage across the first inductor.

Applying the DC voltage across the first inductor may compriseincreasing the DC voltage in increments from a starting DC voltage to atarget DC voltage.

Increasing the DC voltage in increments may comprise increasing the DCvoltage in increments during a number of cycles until the target DCvoltage is reached. In each cycle, the DC voltage may be increased inincrements from an initial DC voltage to a final DC voltage. The initialDC voltage and the final DC voltage may be increased after each cycle.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show how embodimentsof the same may be carried into effect, reference will now be made, byway of example only, to the accompanying diagrammatic drawings in which:

FIG. 1 is a schematic diagram of an existing waveform generator;

FIG. 2 is a schematic diagram of an example waveform generator accordingto the first aspect;

FIG. 3 is a schematic diagram of another example waveform generatoraccording to the first aspect;

FIGS. 4 to 8 are plots showing example simulation results of thewaveform generator according to FIG. 3;

FIG. 9 is a schematic diagram of another example waveform generatoraccording to the first aspect;

FIGS. 10 to 12 are plots showing example simulation results of thewaveform generator according to FIG. 9;

FIG. 13 is a schematic diagram of an example load that the waveformgenerator of the first aspect is arranged to supply waveforms to;

FIG. 14 is a schematic diagram of another example waveform generatoraccording to the first aspect;

FIG. 15 is a schematic diagram of an example system according to thesecond aspect; and

FIG. 16 is a schematic diagram of an example method according to thethird aspect.

DETAILED DESCRIPTION

Referring to FIG. 2, there is shown a waveform generator according tothe first aspect and indicated generally by the reference numeral 200.The waveform generator 200 is configured to generate two waveforms 211,213 of opposite polarity so as to provide a voltage gain across the load207.

The waveform generator 200 comprises a primary side circuit comprising afirst inductor 201.

The waveform generator 200 comprises a secondary side circuit comprisinga second inductor 203, a first output region 231 conductively coupled tothe load 207 and a second output region 233 conductively coupled to theload 207. The second inductor 203 is arranged to be inductively coupledto the first inductor 201. That is, the second inductor 203 ispositioned in proximity to the first inductor 201 such that there is aninductive coupling between the first and second inductors 201, 203.

The first inductor 201 is conductively coupled to the first outputregion 231 so as to supply a first 211 of the two waveforms 211, 213 tothe load 207. The second inductor 203 is conductively coupled to thesecond output region 233 so as to supply a second 213 of the twowaveforms 211, 213 to the load 207. The first and second output regions231, 233 in this example are conductive wires that are conductivelycoupled to the load 207. In this example, the first inductor 201 and thesecond inductor 203 are both conductively coupled to the load 207 viathe first and second output regions 231, 233.

In the example shown in FIG. 2, the first waveform 211 is shown ashaving a peak voltage with a positive polarity. The second waveform 213is shown as having a peak voltage with a negative polarity. Across theload 207, the two waveforms 211, 213 additively combine to supply a peakvoltage to the load 207 which is the sum of the magnitude of the peakvoltages for the two waveforms 211, 213. For example, if the peakvoltage of the first waveform 211 is +250V and the peak voltage of thesecond waveform 213 is −250V, the two waveforms 211, 213 additivelycombine to produce a peak voltage of +500V across the load 207.

The first terminal 202 a of the first inductor 201 is conductivelycoupled to a DC voltage source 209. The second terminal 202 b of thefirst inductor 201 is conductively coupled to the first output region231 which is in turn conductively coupled to the load 207. In addition,the second terminal 202 b of the first inductor 201 is conductivelycoupled to a switch 205. The second terminal 202 b of the first inductor201 is conductively coupled to one terminal of the switch 205, andanother terminal of the switch 205 is conductively coupled to ground G.

The switch 205 is activated by a drive signal which means that theswitch 205 transitions between ON and OFF states depending on the drivesignal.

The switch 205 being activated by the drive signal controls thegeneration of the two waveforms 201, 203. In particular, when the switch205 is in the ON state, current flows through the first inductor 201.When the switch 205 transitions to the OFF state, a voltage rises acrossthe first inductor 201. The first inductor 201 and the second inductor203 are arranged such that when a voltage of a first polarity is appliedacross the first inductor 201, a voltage of the same polarity is inducedin the second inductor 203. As a result, the voltage rising across thefirst inductor 201 causes a voltage having the same polarity to beinduced in the second inductor 203.

The waveform generator 200 may further comprise a controller (not shown)that is arranged to supply the drive signal to the switch 205 so as tocontrol the generation of the two waveforms 211, 213.

The first terminal 204 a of the second inductor 203 is conductivelycoupled to the second output region 233 which is in turn conductivelycoupled to the load 207. The second terminal 204 b of the secondinductor 203 is conductively coupled to ground G.

The load 207 comprises a first terminal 208 a and a second terminal 208b. The first terminal 208 a comprises a first electrode 208 a, and thesecond terminal 208 b comprises a second electrode 208 b. The firstterminal 208 a of the load 207 is conductively coupled to the secondoutput region 233 which is in turn conductively coupled to the firstterminal 204 a of the second inductor 203. The second terminal 208 b ofthe load 207 is conductively coupled to the first output region 231which is in turn conductively coupled to the second terminal 202 b ofthe first inductor 201.

Referring to FIG. 3, there is shown another example of the waveformgenerator 200 according to the first aspect. In this example, the switch205 is a Field Effect Transistor (FET) 205, and in particular is a MetalOxide Semiconductor FET (MOSFET) 205. The second terminal 202 b of thefirst inductor 201 is conductively coupled to the drain 205 a of theMOSFET 205. The source 205 b of the MOSFET 205 is conductively coupledto the ground G. The gate 205 c of the MOSFET 205 is arranged to receivethe drive signal. The other components of the waveform generator 200 ofFIG. 3 are the same as the waveform generator 200 of FIG. 2. The samereference numerals have been used in FIG. 3.

Referring to FIGS. 4 to 8 there are shown the results of a simulation ofthe waveform generator 200 according to FIG. 3. It will be appreciatedthat these figures show just an example simulation and are just used tohighlight an advantageous operation of the waveform generator 200. Inthis example simulation, the drive signal applied to the gate 205 c ofthe MOSFET 205 had a frequency of 25 MHz, a duty cycle of 20%, and apeak voltage of 7V. The DC voltage 209 supplied to the first inductor201 has a value of 60V.

Referring to FIG. 4, there is shown a plot 300 of the voltage waveformapplied across the load 207 as a result of the two waveforms 211, 213.The voltage waveform has peaks of approximately 530V and troughs ofapproximately −60V. It will be appreciated that a high, stable, voltagewaveform has been generated at a high frequency.

Referring to FIG. 5, there is shown a plot 330 of the first waveform 211that is supplied to the second terminal 208 b of the load 207. The firstwaveform 211 has peaks of approximately 300V. The peaks in the firstwaveform 211 correspond with the peaks in the voltage waveform appliedacross the load 207 as shown in FIG. 4.

Referring to FIG. 6, there is shown a plot 350 of the second waveform213 that is supplied to the first terminal 208 a of the load 207. Thesecond waveform 213 has the opposite polarity to the first waveform 211as shown in FIG. 5. The second waveform 213 has peaks of approximately−230V. The peaks in the second waveform 213 correspond with the peaks inthe first waveform 211 as shown in FIG. 5 and with the peaks in thevoltage waveform applied across the load 207 as shown in FIG. 4.

Referring to FIG. 7 there is shown a plot 370 of the voltage across theMOSFET 205. Referring to FIG. 8 there is shown a plot 400 of the firstand second waveforms 211, 213 superimposed over one another. Inreference to FIGS. 7 and 8, it can be seen that the peaks in the firstand second waveforms 211, 213 are a result of the MOSFET 205transitioning from the ON to the OFF state. In addition, it can be seenthat the first and second waveforms 211, 213 are of opposite polarity,and a result cooperate together to produce a larger voltage gain acrossthe load 207. The voltage gain is equal to the sum of the absolutevalues of the voltages for the first and second waveforms 211, 213.

Referring to FIG. 9, there is shown another example waveform generator200 according to the first aspect. In this example, the second outputregion 233 comprises a third inductor 215. The second inductor 203 isconductively coupled to the third inductor 215 which is in turnconductively coupled to the load 207. The first terminal 204 a of thesecond inductor 203 is conductively coupled to the first terminal 214 aof the third inductor 215. The second terminal 214 b of the thirdinductor 215 is conductively coupled to the first terminal 208 a of theload 207. In this example, the first output region 231 comprises afourth inductor 217. The first inductor 201 is conductively coupled tothe fourth inductor 217 which is in turn conductively coupled to theload 207. The second terminal 202 b of the first inductor 201 isconductively coupled to the first terminal 218 a of the fourth inductor217. The second terminal 218 b of the fourth inductor 217 isconductively coupled to the second terminal 208 b of the load 207. Theother components of the waveform generator 200 of FIG. 9 are the same asthe waveform generator 200 of FIGS. 2 and 3. The same reference numeralshave been used in FIG. 9.

While not being bound to any particular theory, the added third inductor215 and/or fourth inductor 217 resonate with the capacitance of the load207. The addition of the third inductor 215 and/or fourth inductor 217result in narrower waveform peaks 211, 213 with a higher peak voltage.This results in a higher voltage being generated across the load 207 forthe same input DC voltage 209 and MOSFET 205. The waveform generator 200of FIG. 9 may have a reduced operational frequency range as compared tothe waveform generator 200 of FIGS. 2 and 3. In addition, slightly moreringing artefacts on the waveforms may be expected than in the waveformgenerator 200 of FIGS. 2 and 3.

Referring to FIGS. 10 to 12, there are shown the results of a simulationof the waveform generator 200 according to FIG. 9. It will beappreciated that these figures show just an example simulation and arejust used to highlight an advantageous operation of the waveformgenerator 200. In this example simulation, the drive signal applied tothe gate 205 c of the MOSFET 205 had a frequency of 25 MHz, a duty cycleof 20%, and a peak voltage of 7V. The DC voltage 209 supplied to thefirst inductor 201 has a value of 60V.

Referring to FIG. 10, there is shown a plot 430 of the voltage waveformapplied across the load 207 as a result of the two waveforms 211, 213.The voltage waveform has peaks of approximately 700V and toughs ofapproximately −60V. It will be appreciated that the peaks of thewaveform are higher and narrower than the waveform shown in FIG. 4.

Referring to FIG. 11, there is shown a plot 450 of the first waveform211 that is supplied to the second terminal 208 b of the load 207. Thefirst waveform 211 has peaks of approximately 370V. The peaks in thefirst waveform 211 correspond with the peaks in the voltage waveformapplied across the load 207 shown in FIG. 10.

Referring to FIG. 12, there is shown a plot 470 of the second waveform213 that is supplied to the first terminal 208 a of the load 207. Thesecond waveform 213 has the opposite polarity to the first waveform 211as shown in FIG. 11. The second waveform 213 has peaks of approximately−330V. The peaks in the second waveform 213 correspond with the peaks inthe first waveform 211 as shown in FIG. 11, and with the peaks in thevoltage waveform applied across the load 207 as shown in FIG. 10.

Referring to FIG. 13, there is shown an example load 207. The load 207is an ion filter device 207, and in particular is a Field Asymmetric IonMobility Spectrometer (FAIMS) 207. FAIMS 207 may be used to distinguishcharged gaseous molecules according to differences in the speed that themolecules move through a buffer gas under the influence of anoscillating electric field.

The FAIMS 207 comprises two electrodes 208 a, 208 b in the form ofparallel plates 208 a, 208 b which are spaced apart so as to define achannel 219. The first parallel plate 208 a is conductively coupled tothe second output region 233 (FIGS. 2, 3 and 9). The second parallelplate 208 b is conductively coupled to the first output region 231(FIGS. 2, 3 and 9). The waveform generator 200 (FIGS. 2, 3, and 9)applies the two waveforms 211, 213 (FIGS. 2, 3 and 9) across theparallel plates 208 a, 208 b which results in an alternating electricfield being applied across the channel 219. In this example, the appliedwaveforms 211, 213 are asymmetric waveforms, meaning that the duty cycleis less than 50%.

In an example application, vapour from a sample to be analysed is firstionized, and then passed through the channel 219 between the twoparallel plates 208 a, 208 b. During the periods when the waveformapplied across the parallel plates 208 a, 208 b has a positive polarity,the ions will drift in one direction at a velocity based on the ionsindividual mobility in that electric field. As the applied waveformreverses in polarity, the ions change direction and speed based on thenew electric field conditions. As the mobility of the ions during thetwo parts of the waveform is rarely equal, there is usually a net drifttowards one of the parallel plates 208 a, 208 b. In the FAIMS 207, thisnet drift is corrected for by applying an additional DC voltage, knownas the compensation voltage, focusing specific ions through the FAIMS207 to the detector.

In the example shown in FIG. 13, it can be seen that three ions 491,493, 495 are introduced into the channel 219 between the two parallelplates 208 a, 208 b. The ions 491, 493, 495 follow a generally saw-toothtrajectory due to the application of the alternating waveform to the twoparallel plates 208 a, 208 b. Due to the different mobility behavioursof the three ions 491, 493, and 495 under the influence of the electricfield, and in particular due to how the mobility of the ions 491, 493,and 495 vary with the electric field strength, each of three ions 491,493, 495 follow a different trajectory in the channel 219. Thetrajectory of two of the ions 491, 493 collide with the parallel plates208 a, 208 b. The ion 495 has the appropriate compensation voltageapplied, meaning that its trajectory traverses the channel 219 of theFAIMS 207. By scanning through a range of magnitudes of waveformsapplied to the parallel plates 208 a, 208 b, and a range of compensationvoltages, and by recording the ion current at eachmagnitude/compensation voltage value, the FAIMS 207 can be used togenerate information about the different compounds present in a sample.

Referring to FIG. 14, there is shown another example waveform generator200. In this example, a compensation voltage is applied to the FAIMS207. The first terminal 208 a of the FAIMS 207 is conductively coupledto a first DC compensation voltage source 241. The second terminal 208 bof the FAIMS 207 is conductively coupled to a second DC compensationvoltage source 239. In this way, a DC compensation voltage is appliedacross the FAIMS 207. The first output region 231 comprises a firstcapacitor 235. The first capacitor 235 has a first terminal 234 aconductively coupled to the second terminal 202 b of the first inductor201, and a second terminal 234 b conductively coupled to the secondterminal 208 b of the FAIMS 207. The second output region 233 comprisesa second capacitor 237. The second capacitor 237 has a first terminal236 a conductively coupled to the first terminal 204 a of the secondinductor 203, and a second terminal 236 b conductively coupled to thefirst terminal 208 a of the FAIMS 207. The other components of thewaveform generator 200 of FIG. 14 are the same as the waveform generator200 of FIGS. 2, 3, and 9. The same reference numerals have been used inFIG. 14.

The first capacitor 235 and the second capacitor 237 may be selectedsuch that they do not have a significant effect on the waveform voltagegeneration. For example, the first and second capacitors 235, 237 mayhave a high capacitance of 10 nF or more so as to cause only a smallvoltage drop. The first and second capacitors 235, 237 are provided toblock DC current flowing to ground G via the MOSFET 205 or the secondinductor 203 as a result of the applied DC compensation voltages. As thefirst and second capacitors 235, 237 are arranged in series with theFAIMS 207, and have high capacitance values, they have a minimal effecton the performance of the waveform generator 200.

The first and second capacitors 235, 237 may be combined with the thirdand fourth inductors 215, 217. That is, the first output region 231 maycomprise the fourth inductor 217 and the first capacitor 235 connectedin series. Either the first capacitor 235 or the fourth inductor 217 maybe conductively coupled to the second terminal 208 b of the load 207. Inaddition, the second output region 233 may comprise the third inductor215 and the second capacitor 237 connected in series. Either the secondcapacitor 237 or the third inductor 215 may be conductively coupled tothe first terminal 208 a of the load 207.

The present invention is not limited to waveform generators 200 forFAIMS 207. Instead, it will be appreciated that the waveform generator200 of the first aspect is ideally suited for the generation ofwaveforms for FAIMS 207. This is at least because the waveform generator200 according to the first aspect is able to generator stable, high peakvoltage waveforms, with a high frequency, and with sharp transitionsbetween the troughs and the peaks of the waveform. In addition, as thewaveform generator 200 of the first aspect can be operated at lowerpower due to reduced parasitic effects, it is ideally suited for batteryoperated, and portable, FAIMS 207.

Referring to FIG. 15, there is shown an example system according to thesecond aspect and indicated generally by the reference numeral 500. Thesystem 500 comprises the waveform generator 200 and the load 207, whichmay be a FAIMS 207.

Referring to FIG. 16, there is shown an example method according to thethird aspect for driving a waveform generator 200 according to the firstaspect.

In step S101, the method comprises supplying a drive signal to theprimary side circuit. The drive signal may be supplied to switch 205(FIGS. 2, 3 9, and 14), and may, in particular, be applied to the gate205 c of the MOSFET 205 (FIGS. 3, 9 and 14). The drive signal may have aduty cycle of less than 50%.

In step S102, the method comprises applying a DC voltage across thefirst inductor 201 (FIGS. 2, 3, 9 and 14). This may comprise increasingthe DC voltage in increments from a starting DC voltage to a target DCvoltage.

An example method of driving the waveform generator 200 (FIGS. 2, 3 9,and 14) when the waveform generator 200 is used to supply waveforms to aFAIMS 207 will now be explained.

In this example, the drive signal supplied to the primary side circuithas a frequency of 25 MHz, a duty cycle of 25% and a peak voltage of 6V.

Initially, the DC voltage supplied to the first inductor 201 has amagnitude 0 V. During the time the magnitude is 0V, the compensationvoltage is scanned through a range of values to allow different ions topass through the channel 219 (FIG. 13). Measurements are taken for eachcompensation voltage.

The DC voltage is then increased to 10 V. During the time the magnitudeis 10V, the compensation voltage is again scanned through the range ofvalues. Measurements are taken for each compensation voltage.

The DC voltage is increasing in increments of 10V until the targetvoltage, which in this case is 60V is reached. During each increment,the compensation voltage is scanned through the range of values andmeasurements are taken.

In this way, the method may drive the waveform voltage to generate arange of compensation voltages during each increment of the applied DCvoltage. This allows for the FAIMS 207 to identify different ions in asample.

In another example, increasing the DC voltage in increments may compriseincreasing the DC voltage in increments during a number of cycles untilthe target DC voltage is reached. In each cycle, the DC voltage may beincreased in increments from an initial DC voltage to a final DCvoltage. The initial DC voltage and the final DC voltage may beincreased after each cycle. For example, a first cycle may be 0, 10, 20,30 and 40V, and a second cycle may be 1, 11, 21, 31 and 41V, subsequentcycles will follow the same pattern until the desired target DC voltage(e.g. 60V) is reached. In this example, the cycling of the DC voltagehelps to minimise the effect on the spectra from any systematic noise ordrift. This may be as a result of charge build-up on the FAIMSelectrodes 208 a, 208 b.

The described and illustrated embodiments are to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiments have been shown and described and thatall changes and modifications that come within the scope of theinventions as defined in the claims are desired to be protected. Itshould be understood that while the use of words such as “preferable”,“preferably”, “preferred” or “more preferred” in the description suggestthat a feature so described may be desirable, it may nevertheless not benecessary and embodiments lacking such a feature may be contemplated aswithin the scope of the invention as defined in the appended claims. Inrelation to the claims, it is intended that when words such as “a,”“an,” “at least one,” or “at least one portion” are used to preface afeature there is no intention to limit the claim to only one suchfeature unless specifically stated to the contrary in the claim. Whenthe language “at least a portion” and/or “a portion” is used the itemcan include a portion and/or the entire item unless specifically statedto the contrary.

In summary, there is provided a waveform generator 200 configured togenerate two waveforms 211, 213 of opposite polarity so as to provide avoltage gain across a load 207. The waveform generator 200 has a primaryside circuit comprising a first inductor 201. The waveform generator 200has a secondary side circuit comprising a second inductor 203, a firstoutput region 231 conductively coupled to the load 207, and a secondoutput region 233 conductively coupled to the load 207. The secondinductor 203 is inductively coupled to the first inductor 201. The firstinductor 201 is conductively coupled to the first output region 231 soas to supply a first 211 of the two waveforms 211, 213 to the load 207.The second inductor 203 is conductively coupled to the second outputregion 233 so as to supply a second 213 of the two waveforms 211, 213 tothe load 207. A system 500 incorporating the waveform generator 200, anda method of driving the waveform generator 200 are also provided.

Although a few preferred embodiments of the present invention have beenshown and described, it will be appreciated by those skilled in the artthat various changes and modifications might be made without departingfrom the scope of the invention, as defined in the appended claims.

Attention is directed to all papers and documents which are filedconcurrently with or previous to this specification in connection withthis application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the steps ofany method or process so disclosed, may be combined in any combination,except combinations where at least some of such features and/or stepsare mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings) may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

The invention claimed is:
 1. A waveform generator configured to generate two waveforms of opposite polarity so as to provide a voltage gain across a load, the waveform generator comprising: a primary side circuit comprising a first inductor; and a secondary side circuit comprising a second inductor inductively coupled to the first inductor, a first output region conductively coupled to the load, and a second output region conductively coupled to the load, wherein the first inductor is arranged to be conductively coupled to the first output region so as to supply a first of the two waveforms to the load, wherein the second inductor is arranged to be conductively coupled to the second output region so as to supply a second of the two waveforms to the load, wherein the first output region comprises a first capacitor, the first capacitor having a first terminal conductively coupled to a second terminal of the first inductor and a second terminal conductively coupled to a second terminal of the load, and wherein the second output region comprises a second capacitor, the second capacitor having a first terminal conductively coupled to a first terminal of the second inductor and a second terminal conductively coupled to a first terminal of the load.
 2. The waveform generator as claimed in claim 1, wherein the two waveforms are continuous waveforms both having the same predetermined frequency.
 3. The waveform generator as claimed in claim 1, wherein the two waveforms are supplied to the load at substantially the same time.
 4. The waveform generator as claimed in claim 1, wherein the two waveforms have a frequency of between 10 and 50 MHz.
 5. The waveform generator as claimed in claim 1, wherein the two waveforms have a peak voltage with a magnitude of between 0.5 and 1500 V.
 6. The waveform generator as claimed in claim 1, wherein the two waveforms have a duty cycle of less than 50%.
 7. The waveform generator as claimed in claim 1, wherein a first terminal of the first inductor is conductively coupled to a DC voltage source, and the second terminal of the first inductor is conductively coupled to the first output region.
 8. The waveform generator as claimed in claim 7, further comprising a switch conductively coupled to the second terminal of the first inductor, the switch being arranged to be activated by a drive signal so as to control the generation of the two waveforms.
 9. The waveform generator as claimed in claim 8, wherein the switch is a Field Effect Transistor (FET) including a drain and a gate, wherein the second terminal of the first inductor is conductively coupled to the drain of the FET, and wherein the gate of the FET is arranged to receive the drive signal.
 10. The waveform generator as claimed in claim 8, further comprising a controller arranged to supply the drive signal to the switch so as to control the generation of the two waveforms.
 11. The waveform generator as claimed in claim 8, wherein the waveform generator is arranged to generate the two waveforms as a result of the switch transitioning from an ON state to an OFF state.
 12. The waveform generator as claimed in claim 1, wherein the first terminal of the second inductor is conductively coupled to the second output region and a second terminal of the second inductor is conductively coupled to ground.
 13. The waveform generator as claimed in claim 1, wherein the second output region is arranged to be conductively coupled to the first terminal of the load, and wherein the first output region is arranged to be conductively coupled to the second terminal of the load.
 14. The waveform generator as claimed in claim 13, wherein the first terminal of the load comprises a first electrode, and wherein the second terminal of the load comprises a second electrode.
 15. The waveform generator as claimed in claim 1, wherein the second output region comprises a third inductor, and wherein the second inductor is coupled to the third inductor.
 16. The waveform generator as claimed in claim 1, wherein the first output region comprises a fourth inductor, and wherein the first inductor is coupled to the fourth inductor.
 17. The waveform generator as claimed in claim 1, wherein the load is an ion filter device.
 18. The waveform generator as claimed in claim 17, wherein the ion filter device is a Field Asymmetric Ion Mobility Spectrometer (FAIMS).
 19. The waveform generator as claimed in claim 1, wherein the first inductor and the second inductor are arranged such that when a voltage of a first polarity is applied across the first inductor, a voltage of the same polarity to the first polarity is induced in the second inductor.
 20. A system comprising: a load; and a waveform generator as claimed in claim 1, configured to generate two waveforms of opposite polarity so as to provide a voltage gain across the load.
 21. A method of driving a waveform generator as claimed in claim 1, the method comprising: supplying a drive signal to the primary side circuit; and applying a DC voltage across the first inductor.
 22. The method as claimed in claim 21, wherein said applying the DC voltage across the first inductor comprises increasing the DC voltage in increments from a starting DC voltage to a target DC voltage.
 23. The method as claimed in claim 22, wherein said increasing the DC voltage in increments comprises increasing the DC voltage in increments during a number of cycles until the target DC voltage is reached, wherein in each cycle, the DC voltage is increased in increments from an initial DC voltage to a final DC voltage, and wherein the initial DC voltage and the final DC voltage are increased after each cycle. 